1. Field of the Invention
The invention relates to a device and method for determining an optimum steering angle in understeer situations of a vehicle.
2. Description of the Related Art
Modern vehicles use electronically controllable motors in the steering train in order, on the one hand, to selectively influence the steering torque to be applied by the driver (power steering systems) and, on the other hand, to selectively set steering angles independently of the driver (superimposition steering systems). In addition to these steering systems which act on the front axle of the vehicle, modern chassis control systems, for example global chassis control (GCC) also use rear axle steering systems for controlling the vehicle dynamics.
In order to influence the steering torque which is to be applied by the driver, various closed-loop and open-loop control structures which are respectively aimed at the specific driving situation are known. For example in the case of oversteering driving situations, closed-loop control on the basis of a yaw rate reference is used (WO 2005/054039 A1) and in the case of braking on μ split open-loop control on the basis of ABS wheel information is used (WO 2005/054040 A1). In the case of understeering driving situations, the steering angle which is present when the situation is detected is “frozen”, i.e. by means of a torque control is to be recommended to the driver that he should not increase the steering angle and as a result make the situation worse. A disadvantage with this concept is that the driver is not provided with any feedback about the maximum possible lateral force.
It would therefore be desirable if the driver could be assisted in such a way that he can set a maximum lateral force at the wheels.
DE 10 2005 036 708 A1 discloses stabilizing means which actuate the steering means as a function of a lateral force coefficient of at least one of the steered wheels in order to set a steering angle which stabilizes the vehicle, in which case the stabilizing means set a slip angle of the steered wheels in such a way that the lateral force coefficient does not substantially exceed the region of the maximum.